Extruder-gear pump combinations of this kind are used for working with thermo-plastic synthetic resins. For many years gear pumps have been used for the production of synthetic fibers. In more recent times, extruder-gear pump combinations have been introduced in extrusion lines for the production of very thin lamina with close tolerances, for the production of single or multi-layer blown or flat foils and in cable extrusion.
Remarkably, these extruder gear pump combinations have found no use in the rubber industry. Obviously it was feared that with the rubber material, the vulcanization of portions remaining from the flow stream would cause machine damage and interruptions with the use of gear pumps. Also, in the rubber industry, the required precision for the products to be produced can far better be attained through the use of extruders in combination with calenders.
In the rubber industry, along with the production of cordage, the production of individual pieces for example, metal-rubber elements, rubber springs and similar products also plays a considerable role. Blanks for the finished parts were heretofore produced through extrusion as a continuous strand which was then cut up by a cutting device down stream of the extrusion head. The blanks thus produced do not have any precision. A higher precision can be obtained through production with a piston extruder. Such piston extruder works charge-wise with prewarmed material which is quite expensive. Also they have the disadvantage that the pressed-out blanks are not always produced as thick and homogenous as is required for precision production. For the blanks for finished parts in the rubber industry must be exact and uniform in the weight, form and thickness as is required for the end product.